The Cytoplasm Flashcards
The cytoplasm is the part of the cell located
outside the nucleus and is:
- enclosed by the cell memrane
- containing organelles of the cell
cytoplasm
Consists of
- 50%: organelles
- 50% cytosol [cytoplasmic matrix]
- few % are inclusions
Define
Organelles
The functional subunits of cells
Organelles are divided into:
Membraneous and non-membraneous
The membraneous organelles include:
including the ones outside of the cytoplasm!
- Nucleus
- Plasma/cell membrane
- endoplasmic reticulum
- golgi apparatus
- transport vesicles
- endosomes
- lysosomes
- mitochondria
- peroxisomes
Non-membraneous organelles include:
- Proteasomes
- Centrioles
- Ribosomes
- Cytoskelton
What is the largest organelle?
Nucleus
Are lysosmes non-mem or mem?
membraneous!
How do we know an organelle is membraneous?
It has a plasma membrane just like the cell itself, dividing the cytoplasm into compartments “rooms”.
What are the 3 components of the cell membrane?
- It has a lipid bilayer
- It is trilaminary (3-layered structure)
- Contains a glycocalyx (cell coat)
What is the structure of the lipid bilayer?
thickness and feature
- it is 8nm thick
- contians membrane proteins
What are the 3 layers considered?
- inner hydrophilic layer (inner phosphate head)
- central hydrophobic layer
- outer hydrophilic layer (external phophate head
What is the structure of the glycocalyx?
and what they’re made of!
- covers the extracellular surface of cell membrane
- formed by the glycosylations (carbohydrates) of membraneous glycolipids, glycoproteins and proteoglycans
What is the function of the lipid bilayer?
- cell boundary
- boundary of membranous organelles, separates organelle environment from cytosol
Why is the function of the lipid bilayer important?
- in organelles: to keep enzymes away from their substrates, controlling metabolic processes.
- in cell membrane: obtains intracellular conc. grad.
Function of Membrane Proteins?
- physiological functions
- ex. ion channels
Function of Glycocalyx
- covers and protects cell
- participates in formation of cell surface receptors
What substances does the cell membrane consist of?
- membrane lipids: 42%
- membrane proteins: 55%
- carbohydrates: 3%
L/M of cell membrane
- too thin to be visualized
- a thin dark line surrounding cells
Where are membrane lipids produced?
In the smooth ER
How are membrane lipids transported?
via the golgi apparatus and brought to the plasma membrane as vesicles where they themselves make up the vesicle’s membrane. They then fuse with the plasma membrane as the lipids are incorporated into the plasma membrane.
Where are membrane proteins produced?
in the rough ER
How are membrane proteins transported to the plasma membrane?
Same way membrane lipids are: golgi apparatus then vesicle then fusion
What membrane lipids aggregate in microdomains?
lipid rafts
What are properties of lipid rafts?
- membrane regions that are thick and less in fluid
- consist of integral membrane proteins unique to these lipid rafts
How are membrane lipids found within the plasma membrane?
- lateral diffusion into liquid 2D lipid sheet (fluid mosaic)
- little spontaneous movement from one leaflet to the other (maintains asymmetry) ex. glycolipids only on outer layer/leaflet
Divisions of membrane lipids?
- phospholipids (50%)
- cholestrol (50%)
- sphingolipids (few %)
Phospholipids are ____ because they have a hydrophobic and hydrophilic end.
amphipathic
Why is the lipid bilayer trilaminary?
- because the hydrophobic ends face other in the centre of the membrane.
- the hydrophilic ends face intra- and extracellular surfaces of the membrane.
Where is the cholestrol found?
between the hydrophobic ends of the phospholipids
Function of phospholipids
Stabilize the viscosity of the membrane
The more the cholestrol,
the less fluid the membrane.
sphingolipids are
amphipathic lipids that take part in lipid raft formation
Do membrane proteins float freely within the membrane via lateral diffusion?
Yes, except for the ones that are anchored to the intra/extracellular structures like the cytoskeleton. Those do not move freely.
How domains can the membrane proteins create?
They divide the cell membrane into domains via tight junctions.
Can lateral diffusion be anywhere?
No, it is confined to a single domain
Divisions of Membrane Protein
- Intergral
- Peripheral
Divisions of integral proteins:
- Transmembrane proteins
- Monolayer-associated proteins
- Lipid-linked proteins
Transmembrane proteins are…
amphipathic, with a hydrophobic part (alpha-helix) that cross the plasma membrane. Can be single or multi-pass. And also a hydrophilic part on the ends.
Monolayer-associated proteins are…
amphitpathic proteins that also have a hydrophobic (alpha helix) part that is embedded within the plasma membrane and a hydrophilic part on the end.
Lipid-linked proteins are…
Covalently bound to membrane lipids.
What are peripheral proteins?
They are on the surfaces of the cell membrane and are non-covalently bound to other proteins or lipids. Mainly found on the inside.
Functions
of Integral Proteins
- Ion channels for passage of ions
- Carriers for transport of substances like glucose and amino acids
- Receptors for action of substances like hormones
- Enzymes
Functions of
Peripheral Proteins
- mainly act as enzymes
note that they are often on the inside of the membrane and attached to integral proteins
To enter the cell, molecules must…
Transverse the plasma membrane
The plasma membrane is permeable to:
- fat soluble molecules
- small uncharged water-soluble molecules
The plasma membrane is impreable to:
- large water-soluble molecules
- charged water-soluble molecules
Molecules that are permeable will…
transverse via simple diffusion.
Molecules that are impermeable will…
need transport proteins to go through it.
Passive transport is driven by…
the electrochemical gradient
Types
Passive transport
- Simple diffusion
- Facilitated diffusion
- Others: Bulk Flow/ Filtration, Osmosis, Solvent Drag
molecules
Simple diffusion
- small uncharged water-soluble molecules
- fat-soluble molecules
Types of
Facilitated diffusion
- Carrier proteins
- Channel proteins
Carrier proteins are divided into…
- uniporters
- symporters
- antiporters
the last two carriers are involved in 2nd active transport.
What do channel proteins do?
create hydrophilic pores through the membrane where large or charged water-soluble molecules can pass.
Leak channels:
simple diffusion; no gate and always open, so doesn’t respond to stimuli.
example
of leak channel
Na+—-K+ pump
example of
small water-soluble molecules that can pass though permeation/ protein channels.
Na, K, Cl, etc.
examples of
lipid-soluble substances that can pass membrane via simple diffusion:
- oxygen
- carbon dioxide
- fatty acids
- glycerol
- urea
What is special about the solubility of oxygen?
It is so highly lipid soluble, it enter the cell at rate like the membrane is not there.
Types of gated channels
- Voltage-gated
- Ligand-gated
Voltage-gated open as a result of…
chnage in electric potential across cell membrane
example
of voltage-gated channels
- Na
- K
- Ca
channels
Ligand-gated open due to…
binding of a chemical substance with receptor on channel protein.
example of
Ligand-gated channel
acetylcholine-gated ion channel at motor end plate of neuromuscular junction
What can carrier proteins (aka pumps) do to drive the passive transport of secondary molecules?
they can build up electrochemical gradients. A great example is the Na/K pump
example of
Faciliated diffusion
glucose and most amino acids use these pumps by binding to a receptor which then widens the inner part of the channel of the carrier protein. This does not need energy.
What are properties unique to faciliated diffusion?
- need a carrier
- have high structural specificity
- have competitive inhibition
- have a maximum limit (saturation)
- are pretty sensitive to temperature changes, since substances bind to the carrier via an enzyme.
What is osmotic pressure?
The pressure needed to STOP osmosis.
What is osmotic pressure determined by?
The number of particles in a solution rather than their size
Why can water travel through the lipid bilayer?
- high in kinetic energy
- very small size
What keeps integral proteins in place?
Their amino acids’ hydrophobic interactions WITH the lipids
Lipid rafts have a higher concentration of…
cholestrol and saturated fatty acids to reduce fluidity.
